This invention relates generally to a wetted parallel plate collecting electrode arrangement for an electrostatic precipitator, and more particularly to maximizing the intensity of the electrostatic collecting field to achive high particulate collection rates.
In two-stage electrostatic precipitators such as for cleaning industrial gas, particulate-laden gas is passed through a charging field produced by a corona discharge which electrically charges the suspended particles. The gas is then passed through a spatially separate electrostatic precipitating field produced between a pair of oppositely charged collecting electrodes, and individual charged particles are attracted to the collecting electrode having the opposite polarity. Typically, the collecting electrodes comprise a plurality of curtain-like plates, with alternate plates grounded and other alternate plates at a high negative or positive potential.
In such electrostatic precipitators, the collected particulate must be removed from the collecting electrodes, either continuously or periodically. One commonly employed approach is by mechanically "rapping" the collecting plates to dislodge the collected particulate so that it may fall into a collection bin. Another method of collected particulate removal is to continuously flow a liquid downwardly over the collection electrodes to carry away the collected particulate. A typical liquid is water. This "wet precipitator" method has an advantage in that there is less of a tendency towards reentrainment of particulate into the gas stream compared to the mechanical rapper method.
However, one drawback in the parallel-plate collecting section of two-stage wet precipitators is the water draining off the bottom edges of the collecting electrode plates tends to be accelerated under the influence of the strong electric field across the interelectrode space to the opposite electrode, thus causing sparking and premature limitation of the operating voltage. For the highest possible particulate collection rate, it is desirable to maximize the intensity of the electric collecting field. With conventional wetted parallel collecting electrode plates, the collecting fields have been found to be limited to approximately 12 KV per inch (4.7 KV per cm) before sparkover at moderate water flow rates. By way of contrast, in a dry collecting electrode configuration, the potential may be in excess of 16 KV per inch (6.3 KV per cm.) without sparking.